Surface smoothness tester



Aug. 5, 1941. H. KOTT 2,251,613

' SURFACE SMOOTHNESS TESTER Filed March 10, 1938 All" ATTORNEYS Patented Aug. 5, 1941 PATENT OFFICE 1 2,251,613 1 SURFACE SMOOTHNESS TESTER Hermann Kott, East Orange, N. 1., assignor to Alco-Gravure Division of Publication Corporation, New York, N. Y., a corporation of New York Application March 10, 1938, Serial No. 195,059

13 Claims.

This invention relates to the determination of relative smoothness characteristics of surfaces, and has particular reference to an improved method of testing the smoothness characteristics of paper surfaces, and apparatus for accomplishing the same.

In the printing art, the quality of the printed product obtained is dependent to a great extent on the smoothness of the paper used in the printing process. By smoothness is meant the evenness or lack of roughness of the paper. A smooth paper is usually characterized by an even surface,'which, if examined closely, appears to be closely dotted with numerous tiny projections. In a rough paper, these projections are relatively large, and are not so closely spaced as in a smooth paper so that the paper has a. rough or coarse texture which can be readily felt when the fingers are rubbed over it.

In accordance with current practice, the pres-' sure of the printing rolls is adjusted at the be-,

ginning of a run to'give the desired tone on the paper and is not changed thereaften, So long as the smoothness of the paper remains the same, a uniform product obtains, and no further adjustment of the pressure on the printing rolls is necessary, If, however; the smoothness of the paper changes, as might occur where a number of rolls of paper are used successively,

it has been found thatthe copies printed from the successive roll-s do not have the same tone as those which were printed before. For example, where the paper in the second roll is not so smooth as that previously used, it will be" found that the boundaries between differently colored portions of the printed matter are not as sharply defined as before. Furthermore, delicate tints, especially the flesh colors or light blues,

are found to be considerably darker in tone on a the rougher paper.

This results from the fact that the ink from the plates is applied only to the tips of the projections on the paper surface, and since in a rough paper the effective area in contact with the printing cylinder per unit area of paper is less than in a smooth paper, the ink density is much greater than it would be on a smoother paper and consequently, the tones are darker ous paper surfaces, which can be used to determine the relative smoothness of the printing paper rolls before they are put into the press. The relation between the relative smoothness of the paper and the printing roll pressure necesl5 sary to obtain a product of required definition,

and tone may be easily obtained by conducting a number of simple tests. Knowing this relation and the relative smoothness of the paper, a printed product of the desired definition and tone can always be obtained, and the disadvantages of the present hit-or-miss system avoided.

An object of this invention accordingly is to provide a simple apparatus for measuring the relative smoothness of paper surfaces.

2 A further object of the invention is to provide an improved method and apparatus for measuring relative smoothness in which the smoothness of an unknown surface is measured in terms of its ability to reflect light after an ink impression of standard pressure has 7 been made on it.

Another object of the invention is to provide an apparatus of the above character wherein the smoothness of a paper surface is tested photoelectrically.

Another object of the invention is to provide an apparatus of the above character in which the smoothness of the paper surface is determined'by a null measurement 40 In a preferred embodiment of the invention two beams of substantially identical intensity are directed from a constant source of light upon the opposite faces of the sample to be tested,

and the light reflected from the surfaces of the; test object is then directed to a photoelectric cell. The two light beams originating from the source are alternately interrupted in such fashion that the rays falling on the photoelectric cell from each beam vary sinusoidally with time and are 180 out of phase, so that equal areas of the photoelectric cell are illuminated alternately. One side of the surface to be tested is smudged with ink so that it appears darker than the cleansurface, the degree of darkness depending di- .rectly on its smoothness. light now reflected from the smudged surface is considerably less than that reflected from the clean surface, thus producing an alternating current in the circuit of the photoelectric cell. The alternating current is then amplified in a special balancedamplifier until it is of sufficient magnitude to operate an indicating meter. 6

The beam of light which is directed on the clean side of the test surface is now reduced in area by means of-aniris diaphragm until the reading of the indicating meter is brought to zero, at which point the beams of light reflected from the smudged surface and the clean surface are equal.- The relative smoothness of the surface may then be read directly from the iris diaphragm which may be suitably calibrated toread percentage smoothness. L

Since a null method is used in which the readings do not depend upon the indication of the meter in the amplifier circuit, the determinations made will be independent of errors due to any non-linearity in the response of the photocell or the amplifier circuit itself.

The invention may be better understood from the following detailed description and the accompanying drawing; in which:'

Figure 1 is an apparatus for testing the smoothness of paper surfaces, constructed in accordance stantially constant intensity is shown at l0, from which light is directed through condensing lenses i I in an elongated cylindrical tube I! to form light beams therein. Light also passes from the source I0 to a prism 13 which serves to direct light through the condensing lenses hi to provide light beams in the elongated cylindrical tube It which is disposed parallel and adjacent to the tube l2. In front of the tubes l2 and I! a circular disc I6 is located, in which the staggered apertures I! and I8 are formed. These apertures are so disposed that when the apertures ll permit the passage of light from the tube IS, the passage of light from the tube I2 is prevented, and vice versa.

A second pair of tubes i8 and 20 are mounted on the other side of the disc l8 coaxially, respectively, with the tubes l2 and ii. The tubes l9 and 20 are provided with lenses 2| and 22, respectively, which serve to focus light upon the prisms 23 and 24, respectively, from which light is reflected through the lenses 25 and 26, respectively, to the faces '21 and 28 of the test surface I 29 which is disposed between the two systems and parallel thereto. The light reflected from the face 21 is directed through a lens 38 and prisms 8|, 82 and 83 and through a diaphragm 34 to the surface of a photoelectric cell 85 and the light reflected from the face 28 is directed through a lens 86,

. prisms 31, 88 and 39 and through the diaphragm are 180 out of phase, so that if the two sides 21 and 28 have the same degree of smoothness, a constant amount of light will fall on the photoelectric cell and a direct current will pass through its circuit. I Referring to Figure 3, a balanced amplifier circuit is shown for amplifying current impulses from the photoelectric cell which is of a well known type and therefore need be described only briefly. The photoelectric cell current impulses pass through a wire 38', and the blocking condenser 14, to a grid resistor 15 across which an alternating voltage appears which is impressed on an amplifying tube 16. The amplified voltage is developed across the plate resistor 40 and is then impressed on the grid resistor 4| through a blocking condenser 42, so that the amplifiedvoltase is applied to the grid of a second tube 43. The indication is made by a meter 44 which is placed across the plate and screen grid leads of the tube 43 and. which can be adjusted to a zero position by means of the variable resistors 48 and 41 in series with the plate and screen grid, respectively. The power for the amplifier is supplied from step-up transformer 48 which provides a source of high voltage alternating current. This voltage is rectified by the electronic rectifier 49 and is thereafter filtered in a twosection filter comprising the reactor 68 and a variable resistor 56 in series, and the condensers 52, 53 and 5% in parallel. This two-section filter filters out the alternating components of the pulsating direct current deliveredby the rectifier 49, so that a substantially constant direct voltage is obtained at the output which is then impressed on a voltage regulator tube 55 of a well known type. Thus a substantially constant voltage is supplied through the wire .58 to the screen grid andplate of the tube 48 through the variable resistors 41 and 48, respectively. The same wire also delivers voltage to the plate of the amplifying tube 18 through the plate resistor 48 and a single section filter comprising the series resistor 81 and shunt condenser 58.

Voltage is also supplied .to the screen grid of the tube 18 through a voltage dropping resistor 62 and a single section filter comprising a series resistance 68 and shunt condenser 8|. The same wire also supplies voltage through a voltage dropping resistor 63 for polarizing the photoelectric cell 85. The voltage dropping resistor 63 and the photoelectric cell 35 are shunted by a condenser 64 which serves to provide a low reactance bypass for any alternating current components which may still be present in the direct current supply. 7

Voltage for biasing the grid of the amplifying tube 16 is provided by variable resistor 65 across which part of the output of the voltage regulator tube 55 is impressed. The biasing voltage for the grid of the tube 43 is similarly supplied by means of a variable resistor which is connected in parallel with the resistance 65. The resistances 65. and 68 are shunted to ground by the bypass condensers 81 and 88, respectively.

which tend to prevent undesirable degenerative.

filtering is provided bythe condenser 88' which is connected across the output of the voltage regulator tube 55 so that a direct current voltage is obtained at its terminals which has substantially no alternating current ripple.

The meter which is connected across the screen grid and plate terminals of the tube 43 is adjusted to give a zero reading when both. light beams are of the'same intensity, the adjustment being made by the variable resistors 48 and 41. h

This amplifier is well known for its stable and unvarying characteristics, a feature which makes. it very suitable for amplifying photocell impulses of small'magnitude.

-In an actual test, one side of the test piece ,29, for example, the side 21, is placed beneath an ink stencil to which a fixed pressure is applied so that its surface is smudged with ink. It is. then put in the testing apparatus in the position shown in Figure 1, so that less light is reflected from the surface 21 than from the surface 28. Under these conditions, there are two slnusoidally varying beams of light-falling on the photoelectric cell which are 180 out of phase, one of which is of greater intensity than the other. As a resulteof the change in the light reflected from the two, surfaces, the total light falling on the photoelectric cell valries.

sinusoldally with time, so that an alternating.

current flows in the circuit of therphotoelectric cell 35. This alternating current is amplified by the amplifier described above, causing the meter 44 to give a positive indication whichpmay be used as a measure of the relative smoothness of the paper, if desired. It is preferred,-however, to reduce the area of the beam of light directed onthe 'clean surface 28 by operating an iris diaphragm 13, until the reading of the meter 44 is reduced to zero. The relative smoothness of the paper may then be directly read from markings on the diaphragm 13 which can be calibrate to read a measure of smoothness directly. he advantage of the latter null method of measurement is that it is independent. of-

errors which might be introduced due to nonlinearity of the photocell or its amplifier, or errors in the indicating meter.-

It is evident from the foregoing that the invention provides an improved apparatus by,

means of which the smoothness of a paper surface may be readily determined and paper samples of varying degrees of smoothness may be easily and effectively compared. An importantfeature of the invention is that all determinations aremade by a null measurement so that no errors areintroduced due to non-linearity determine the relative smoothness of the faces of said specimen. w

2.- The method of measuring the relative smoothness of the surfaces of a specimen, comprising smudging one face of a specimen with ink at a predetermined pressure. directing a beam of light from a source to the smudged face,

direct g a second beam of light from the same source 0 the clean face, adjusting the intensities of the lfght beams reflected from said surfaces to a predetermined relation and comparing the adjustment with a standard adjustment to measure the smoothness of the faces of said specimen. r r

3. The method of measuring the relative smoothness of the surfaces of a specimen, comprising smudging one face of a specimen with ink at a predetermined pressure, directing a beam of light from a source to the smudged face,

directing a second beam of light from the same sourcetojthe clean face, interrupting the said light beams alternately, directing the light reflected from both said faces to a photosensitive device to produce current impulses therein. am-

plifying the said photosensitive device current impulses, determining the magnitude of the said amplified current impulses adjusting the intensity of at least one light beam until the current impulses are of a predetermined magnitude, and comparing the adjustment of said light beam with a standard adjustment to determine the relative smoothness of the faces of said specimen. I

4. The method of measuring the relative smoothness of the surfaces of a specimen, comprising smudging one face of a specimen with 'lnk at a predetermined pressure, directing a of the photoelectric cell or the amplifying sys- I tem. The embodiments and methods described above are obviously capable of numerous changes in form and detail within, the scope of the invention and it is not intended to be in any way limited thereby except as defined in the appended claims.

I claim: 3 l. The method of measuring the relative smoothness of the surfaces of a specimen, comprising smudging one face of a specimen with ink at a predetermined pressure, directing abeam of light from a source to the smudged face, directing a second beam of light from the same source to the clean face, alternately interrupting the said light beams, directing the light refiected from both said faces to a photosensitive device to produce current impulses therein rang-v ing in magnitude from zero when the reflected light beams are of equal intensity to a maximum when the beams are of maximum inequality in intensity, and comparing the magnitude of the beamgof light from a source to the smudged face, directing a second beam of light from the same source to the clean face, interrupting the said light beams alternately, directing the light reflected from both said faces to a photosensitive device to produce current impulses therein, amplifying the said photosensitive device cur- I rent impulses, measuring the magnitude of the said amplified current impulses,. adjusting the cross sectional area of at least one of the said light beams to reduce the measured current impulses to a predetermined value and comparing the adjustment of the area of said light beam with a standard adjustmentto determine the beams reflected from the said surfaces. means for equalizing the intensities of the reflected light beams, and means calibrated in degrees of relative smoothness actuated with said equalizing means for indicating the smoothness of the said paper surfaces when the intensities of the current impulseswith a standard magnitude to light beams are equal.

6. A device for measuring the relative smoothness of paper surfaces comprising a light source, means ,to direct a beam of light from the light source to one surface of the said paper. means to direct a second beam oflight from the light source to the opposite surface of the said paper,

means for varying the said light beams sinusof said'beams, and means calibrated to indicate variations in smoothness v actuated with said equalizing means for indicating the smoothness,

of said paper surfaces when the intensities of the light beams are equal.

'l. A device for measuring the relative smoothness of surfaces of a specimen, comprising, a light source, means to direct a beam of light from the light source to one face of the specimen, means to direct a second beam of light from the light source to. another face of the said specimen, means for varying said beams in opposite phase relationship, means responsive to differences inthe intensities of the light beams reflected from the said faces for indicating the variations in the relative intensities of the reflected light beams caused by variations in the reflecting power of the said specimen faces.

8. A device for measuring the relative smoothness of surfaces of a specimen, comprising a of the reflected light beams caused by variations in the reflecting power of said surfaces and means for equalizing the intensities of said reflected light beams said equalizing means being calibrated in terms of smoothness of the specimen faces.

9. A device for measuring the relative smoothness of surfaces of a,specimen, comprising a light source, means to direct a beam of light from the light source to one face of the specimen, means to direct a second beam of lightfrom the light source to another face of the said specimen, means to vary the said beams substantially slnusoidally with time and in opposite phase relationship, a photosensitive cell responsive to the'light beams reflected'from the said specimen faces and means actuated by said photosensitive cell" for indicating unequal energization of the said cell by said beams.

10. A device for measuring the relative smoothness ofsurfaces of a specimen, comprising a light source, means to direct a beam of light from the light source to one face of the specimen, means to direct a second beam of light from the light source to another face of the said specimen, means ii 'tuated by said photosensitive cell for indicating unequal energization of the said cell by the said beams, and means for adjusting the area of at least one of the said light beams to equalize the reflected intensities thereof, said adjusting means being calibrated to indicate variations in smoothness.

11. A device for measuring the relative smoothness of surfaces of a specimen, comprising a light source, means to direct a beam of light from the light source to one surface of the specimen,

means to direct a second beam of light from the light source to another surface of the specimen, a rotatable disk having apertures formed therein in the respective paths ofthe said light beams, the apertures in each path being staggered with respect to the apertures in the other path, means for rotating the disk to vary the beams sinusoidally with time and in opposite phase relationship, means to direct the light beams reflected from the said surfaces to a photosensitive cell, and means actuated by said photosensitive cell for indicating variations in the relative intensities of the light beams reflected by said surfaces.

12. A device for measuring the relative smooth- 80 ness of surfaces of aspecimen, comprising a light source, means to direct a beam of light from the light source to one surface of the specimen, means todirect a second beam of light from the light source to the opposite surface of the-specimen, a

3 rotatable apertured disk for interrupting the said light beams alternately, means to direct light reflected from both of said surfaces to a photosensitive cell, means actuated by said cell for indicating unequal intensities of the reflected beams and an iris diaphragm for adjusting the crosssectional area of one of the said beams to equalize the intensities? of the reflected beams. 13. A device for measuring the relative smoothness of specimen surfaces, comprising a light source, means to direct a beam of light from the light source to one surface of the specimen, means direct a second beam of light from the light source to the opposite surface of the said speci men, a rotatable apertured disk for interrupting iii) the said light beams alternately, means for rotating said disk, reflecting means to direct light reflected from both said surfaces to a photosensitive cell, means to amplify the impulses from the said photosensitive cell, means in the circuit of the amplifying means for indicating unequal intensities of the beams reflected from said sur-, faces, an iris diaphragm for varying the crosssectional area of one of the said light beams to equalize their reflected intensities and a scale on said diaphragm for indicating the smoothness of 

